[TheDong]

Absolutely. If you watch the youtube video linked in this thread, SPJ makes that very comment, that a program with zero effects is useless.

However, the goal of haskell (and indeed any language trying to be safe in the way SPJ means) is to be able to have most code be safe/effect-free, and then to have effects be very carefully controlled and limited in their use. Things like the IO monad mean many parts of haskell code can't do IO in fact.

We obviously do want some sort of effect in the end, but the idea is it's safer to contain those effects in very limited places, and not allow effects to happen literally anywhere at any time.

Note, unsafe in the SPJ video was specifically about effects, while "unsafe" in rust terminology is mostly about memory safety, so those two terms really aren't the same word, and to be honest that can make communication less clear. I don't know what "category of unsafe" meant in your comment really.